Ventricular depolarization and repolarization of the heart muscle, represented by QT intervals detected by an electrocardiogram (ECG), is an important variable for the prediction of sudden cardiac death or ventricular arrhythmia, known as Torsade de Pointes (TdP), and is used for the classification of patients with long and short QT intervals. All medication must be tested in order to find out whether or not it has an effect on QT intervals. There is a relation between QT intervals and heart rate, defined by RR intervals. Analysis of the QT/RR coupling is one of the primary problems in the evaluation of QT interval abnormalities and the effect of medication on QT intervals. In spite of the fact that a lot of research units are investigating this issue, there is no model or comprehensive list of parameters describing the static and dynamic characteristics of the QT/RR coupling.
QTc is the basic parameter in use. It is a recalculated QT interval for the RR interval, which equals 1 second. The QTc parameter is calculated by means of a non-linear static correction considering the dependence only on the previous RR interval. Many corrections based on various types of non-linear static function have been proposed. Bazett's correction, derived as far back as 1920, is still the most commonly used, but also the most criticized. It has been shown that QTc is not an adequate parameter for characterization of ventricular depolarization and repolarization: it is merely a static parameter. The dynamic characteristics of the connection are not considered in QTc calculation, although it is known that TdP is induced by a sudden change in RR intervals caused, for example, by stress or physical strain. A large number of published corrections also raise doubts about the correct calculation of the QTc value by means of non-linear, static dependence.
Other parameters used to characterize QT/RR coupling are the delay with which QT attains a steady state, QT “dynamics”, QT/RR variability, and graphic analysis. Porta and Almeida used a higher order transfer function, with eight or more parameters, to characterize QT/RR coupling during individual measurements, with the selected function order being optimized for a given measurement. The number and type of parameters applied were different for individual measurements. However, they analyzed only short measurements at rest. They were not able to define a general model and characteristics of QT/RR coupling. There is no comprehensive set of parameters that would enable an objective assessment of ventricular repolarization of a particular subject or an objective evaluation of the effect of medication.
Ventricular repolarization is sometimes analyzed from other intervals detected from ECG, such as RT, RTmax and QTmax intervals. The problems facing evaluation are the same as those for the QT interval.
The aim of this invention is to provide a method that would enable an integrated set of parameters describing the static and dynamic characteristics of repolarization to be obtained. This set of parameters would be used for evaluation of the effect of medication on patients' health.